The emergence of global terrorist threats and a marked increase in the smuggling of contraband has created the need for systems and methods to detect explosives, flammable liquids, chemical warfare agents, and illegal or controlled drugs in public locations. For example, security personnel in locations such as airports, building and stadium entrances, military and government facility checkpoints, and customs checkpoints must now have the ability to quickly and accurately scan items and persons, and determine whether any of the above described contraband is present. Currently, various invasive and non-invasive systems and methods are employed, but none of these conventional systems and techniques is capable of accurately distinguishing water-based liquids from organic liquids in a variety of liquid containers.
For example, ultrasonic reflection techniques at one or more ultrasonic frequencies are used to characterize liquids, to some degree, by analyzing the speed of sound travel through, and heat capacity of, liquids under inspection. Such ultrasonic reflection techniques measure such parameters as ultrasonic velocity, attenuation, reflection coefficients, and scattering amplitudes, which are related to fundamental physical properties of fluids and slurries of interest to food processors and manufacturers of consumer products. Non-invasive ultrasonic methodologies have been developed that offer on-line, real-time analysis of many physical properties, including fluid viscosity, density, sheer rate, particle size distribution, concentration, settling and plug formation, fouling and pipeline wall buildup detection, liquid-liquid interface detection, and some low specificity chemical identity confirmation. Many of the ultrasonic reflection methodologies mentioned above have developed into practical monitoring devices.
Conventional ultrasonic instrumentation (measuring) devices, as discussed above, are well-established performers in a myriad of industrial applications. Several new ultrasonic systems with applications to the food industry have been developed, including an ultrasonic rheometer, an ultrasonic densimeter, and an ultrasonic liquid characterization device. These ultrasonic systems were initially developed in response to environmental and national needs to non-invasively measure the physical properties of liquids and slurries.
U.S. Pat. No. 5,767,407 describes a method for rapid, noninvasive identification and monitoring of chemicals in sealed containers or containers, where direct access to the chemical is not possible. Multiple ultrasonic acoustic properties (up to four) of a fluid are simultaneously determined. The method described in U.S. Pat. No. 5,767,407 can be used to provide some chemical identification information, and for determining changes in known chemicals from a variety of sources. However, the method described therein does not provide for identification of all known chemicals, only those identifiable based on certain measured parameters, and only known classes of chemicals in suspected containers, such as in chemical munitions, can be characterized. In addition, a significant number of industrial chemicals can be identified.
However, ultrasonic sensing is not very selective, and can only differentiate liquids by properties such as viscosity, and the speed of sound, which can result in ambiguity in distinguishing certain organic liquids from water. Furthermore, the presence of particulates, such as those present in baby formula, can interfere with the sensing process. In addition, when using the ultrasonic sensing approaches described above, problems may be encountered with containers having irregular shapes, or having a small radius of curvature which would not interface well with a flat or fixed geometry probe transducer surface. Conventional ultrasonic reflection techniques have been found to be not as selective as near-infrared spectral characterization techniques at one or two near-infrared wavelengths, and are not capable of quickly and accurately distinguishing water-based liquids from organic compound-based liquids, as required in security applications.
Similar to ultrasonic liquid inspection is electromagnetic radio or microwave frequency dielectric constant monitoring devices, which measure differences in dielectric constants. Dielectric constants vary between different liquids, but will not necessarily be unique for every liquid of interest. Like ultrasonic techniques, dielectric sensing is not highly specific to molecular structure, and occasionally fails to distinguish certain organic liquids from water. Also, thick bottle or container walls can interfere with the accuracy of dielectric sensing. Further, dielectric sensing techniques sometimes encounter problems when analyzing containers having irregular shapes or a small radius of curvature, which does not interface well with a flat probe transducer surface.
Another conventional technique used to identify compositions is Laser-Raman spectroscopy. This technique can be used for selective chemical identification of liquids contained inside of clear containers, but has difficulty when inspecting containers with pigments in the walls of said containers, or in penetrating labels on the containers, if the pigments in the container walls or labels are strongly absorbing, scattering or fluorescent at the laser wavelength (which is usually about 785 nm). Specifically, pigments contained in the bottle or container wall, or in labels and paper in labels, can interfere through light scattering or optical absorption of the laser light, which is typically at 785 nanometers (nm) for lower cost and portable laser-Raman systems, or by fluorescence induced by the laser. Further, Laser-Raman spectroscopy involves expensive instrumentation which can be temperature and vibration sensitive.
A further conventional inspection technique is X-ray fluorescence spectroscopy. This technique can provide elemental analysis information about a liquid contained inside of a bottle. However, X-ray fluorescence only determines the atomic composition, and is not sensitive to elements with atomic numbers less than sodium (Na). The X-ray fluorescence emission corresponding to elements lighter than Na is absorbed by small path lengths (i.e. 2 mm) through air, and requires the sample be placed in a vacuum container to be detected. As such, X-ray fluorescence cannot be used to detect hydrogen, oxygen, nitrogen, or carbon, all of which must be detected to differentiate water from organic liquids in general.
In view of the deficiencies of the conventional inspection techniques, as discussed above, it is an object of the provide a system and method capable of detecting and distinguishing organic from aqueous liquids, disposed inside of vessels capable of transmitting NIR light.
It is another object of the present invention to provide a system and method to distinguish organic from aqueous liquids inside of such vessels with enhanced contrast and reduced interference from labels disposed on the vessels.
It is yet another object of the present invention to provide a system and method to distinguish organic from aqueous liquids for liquids in such vessels containing substantial concentrations of particulates or emulsions.
It is another object of the present invention to provide a system and method to detect the presence of an organic or other hazardous liquid present in a smaller vessel that is concealed within a larger vessel that holds an aqueous liquid.
It is another object of the present invention to provide a system and method to simultaneously inspect groups of two or more vessels, so as to be capable of detecting the presence of a hazardous liquid in one or more of the vessels.
It is yet another object of the present invention to distinguish organic from aqueous liquids for liquids in vessels containing substantial concentrations of particulates or emulsions, by differential wavelength NIR reflectance imaging (between 980 nm and 1050 nm, 980 nm and 920 nm, or other pairs of wavelengths corresponding to peak water absorptions and adjacent off-peak wavelengths). Differential wavelength imaging, involving the technique of subtracting an image of an object measured at a first wavelength band from an image measured at a second wavelength band, where the position of the object relative to the camera is the same for both image measurements, enables same.
It is another object of the present invention to detect the presence of an organic or other hazardous liquid present in a smaller vessel that is concealed within a larger vessel that holds an aqueous liquid, using single or differential wavelength NIR transmission or reflectance imaging. In addition to the wavelengths of 920, 980, and 1050, other wavelengths may be used for the NIR image detection of vessels of organic liquids concealed within larger vessels holding aqueous liquids.
It is another object of the present invention to provide an imaging system and method to inspect one or more vessels capable of transmitting NIR light, determine the peak absorbances of the light transmitted or reflected therefrom, compare the measured peak absorbances to a database of known absorbances of liquid explosives, and determine whether a known liquid explosive is contained in the vessel, and what liquid explosive it is.